Recent years have witnessed the advent of Radio Frequency (RF) circuits requiring filters with High Q factors and sharp stop bands. Existing systems are capable of providing filters with High Q factors and stop bands to RF circuits.
One existing system employs SAW filters to provide filters with High Q factor in the RF circuits. SAW filters are filters with high Q factors and sharp stopbands. However, use of the SAW filter in RF circuits is associated with several drawbacks. Firstly, the SAW filters are too bulky to be realized on-chip. As a result, the SAW filters are implemented externally. The SAW filters increase the size and cost of the RF circuits. Further, insertion loss of the SAW filters adds to the noise figure of the RF circuits. Moreover, impulse response, filter bandwidth and center frequency of the SAW filter lack programmability. As a result, the RF circuits require a different SAW filter for every frequency, band and mode of operation. Moreover, the drawbacks of the SAW filter make the RF circuit bulky and expensive. As a result, there is a need for a low cost on-chip system capable of providing function of a High Q filter in a RF circuit. Existing systems employ a plurality of methods to simulate functioning of the High Q filter in an RF circuit.
In another existing system, an RF circuit uses mixers, notch filters, amplifiers, and signal subtractors to simulate a filter in the RF circuit. In an example, a mixer in the RF circuit converts an RF signal at radio frequency to an IF signal at Baseband frequency. Further, system feeds the IF signal simultaneously into a first path and a second path. The first path includes a first amplifier. The IF signal fed into the first path is a first signal. The first amplifier amplifies the first signal. The second path includes a notch filter and a second amplifier. The IF signal fed into the second path is a second signal. The notch filter allows undesired frequency bands of the second signal to pass through and attenuates desired frequency bands of the second signal. Further, the second amplifier amplifies the second signal. A signal subtractor subtracts the second signal from the first signal. As a result, output of the signal subtractor lacks the undesired frequency bands. In effect, the system frequency translates the low Q baseband filter to a high Q notch filter. However, the system has several disadvantages. Impulse response of the notch filter lacks programmability. Further, use of the signal subtractor, the first amplifier, and the second amplifier adds to the noise figure of the system.
In yet another existing system, an RF circuit uses the impedance transformation property of passive mixers to generate a High Q band pass filter from a low Q baseband impedance. Center frequencies of the high Q band pass filters are governed by frequency of a local oscillator fed into the passive mixer. The system generates the high Q filter using a passive mixer based on switches and a low Q baseband impedance. In an example, the low Q baseband impedance are capacitors. However, impulse response of the High Q filters generated lack programmability.
One solution to problems displayed by existing systems is synthesizing impedance in an RF amplifier in the RF circuit thereby altering frequency response of the RF amplifier to frequency response of a High Q band pass filter.
In light of the foregoing discussion, there is a need for a system to synthesize a High Q impedance in an RF amplifier and thereby altering frequency response of the RF amplifier to frequency response of a High Q band pass filter. It is desired that the system enables synthesis of high Q impedance in the RF amplifier via impedance transformation of low Q baseband impedance. Moreover, it is desired that the synthesized high Q impedance in the RF amplifier is programmable. Further, it is desired that the central frequency of frequency response of the RF amplifier is programmable. It is desired that the impulse response of the high Q impedance filter is programmable. It is also desired that any type of filter be incorporated into the RF amplifier through impedance transformation.